Conventional forced air residential and commercial air conditioning systems often include humidifiers for maintaining proper relative humidity in the system supply air, typically during the heating season in certain climates but also during year-round operation in certain other climates. One widely used type of humidifier is known as a bypass type which is typically configured such that the humidifier unit itself mounts on the system supply air plenum or cabinet, typically downstream of the furnace heat exchanger and the system cooling coil or evaporator. At least a portion of the conditioned air flowing through the plenum is bypassed through the humidifier and through a so-called bypass duct to the return air plenum upstream of the system cabinet. In this way, a suitable pressure differential is maintained by the system blower or fan to provide for air flow through the humidifier.
During operation of the system wherein cooling of the supply air is required, the bypass duct is closed by a manually actuated damper, typically constructed as a butterfly type valve closure member with a manual lever for moving the closure member between open and closed positions. However, the homeowner or system operator often forgets to move the damper to the closed position during operation of the system in periods of ambient climate conditions wherein humidification of the system supply air is normally not required. Thus, there has been a need to provide for automatic control of the damper to provide for closing same when humidification of the supply air flowing through the air conditioning system is not required. It is to these ends that the present invention has been developed.